1. Technical Field
The present invention relates to USB devices, particularly to USB peripheral devices, such as card readers, for portable host devices, such as smart phones or tablet computers.
2. Related Art
USB (Universal Serial Bus) was designed to standardize the connection of computer peripherals, such as keyboards, pointing devices, digital cameras, printers, portable media players, disk drives and network adapters to personal computers, both to communicate and to supply electric power. It has become commonplace on other devices, such as smartphones, PDAs and video game consoles. USB has effectively replaced a variety of earlier interfaces, such as serial and parallel ports, as well as separate power chargers for portable devices. It can be said that USB is the most popular interface in the world.
The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire from which connected USB devices may draw power. In recent years, more and more countries prescribe that all mobile phones sold in those countries are required to use the USB port as a power port. Also, many standard-setting organizations, such as the Open Mobile Terminal Platform group, the GSM Association (GSMA) and the International Telecommunication Union (ITU), announce that their members have agreed on micro-USB as the future common connector for mobile devices and a standard charger for mobile phones. The standard connector to be adopted is to be the micro-USB connector. Having a standard charger for all phones means that manufacturers will no longer have to supply a charger with every new phone. Thus the micro-USB connector is and will be a primary interface port for both communication and power charge or supply.
Generally, a portable host device, such as a mobile phone or tablet computer, is equipped with only one micro-USB port for connecting either a peripheral device or a charger. That is to say, a charger cannot be plugged in if a peripheral device has occupied the micro-USB port, and vice versa. Obviously, users have to frequently plug and unplug a peripheral device or charger. This is so inconvenient for users.